It is known to provide a rotatably wheel structure for propelling abrasive grit or the like radially outwardly thereof, the grit being supplied to a central opening in the rotatable wheel structure and propelled outwardly by the rotary movement of blades mounted on the wheel. Because of the destructive nature of the material being handled, it is necessary to replace the blades from time-to-time, and various assemblies have been developed to permit such replacement.
One structure of this general type is shown in German Pat. No. 21 15 354, (which corresponds to U.S. Pat. No. 3,745,711) in which the blades are inserted from outside the wheel and where the wheel has rotatable stops. Stops which can be plugged in are shown in Swiss Pat. No. 352,923, (which corresponds to U.S. Pat. No. 2,819,562) and in either of these cases, marginal strips along the edges of the blades and the cooperative grooves in the wheels are formed with parallel sides. During the operation of the wheels, the abrasive or blasting material being propelled thereby is deposited in the cracks of the grooves between the discs and the blades, leading to a wedging of the grains of the blasting medium in these cracks. This complicates and makes difficult the dismantling of the blades which are, as indicated, subjected to considerable wear. Often it is necessary to dismantle the blades by striking the structure repeatedly with a hammer since it is necessary to extract the blades from the entire length of the grooves.
This is detrimental to the wheel itself, and particularly to its mounting. In addition, the space in the center of the wheel is very limited for the task of removing the blades. Moreover, the blades, the throwing surfaces of which consist of hard metal, must not be damaged by such hammer blows since, in that case, the blades will be damaged and further use of the opposite surface, in cases where the blade is reversible, is made impossible. The Swiss Pat. No. 352,923 shows recesses on the lateral strips of the blades which were intended to improve the removal, but it has developed in practice that the recesses or pockets are similarly filled with blasting material during the operation, and the grains of the material are compressed in such a way that no considerable improvement of the blade removal was achieved.
Other wheels of the general type discussed herein have been known wherein the blades are inserted from the center of the fly wheel into the grooves, the blades having fixed stops on the blade or on the wheel disc. Examples of these are found in German Pat. No. 21 12 497 (which corresponds to U.S. Pat. No. 3,683,556) and German Offenlegunsschrift No. 26 34 198 (which corresponds to U.S. Pat. No. 4,069,025). Because of the grooves and lateral strips which are formed in parallel with each other, the above-described difficulties occur when attempting to remove the blades from the outside to the inside. Also, the sections of each lateral strip, described in OS No. 26 34 198, do not simplify the blade removal for the reasons mentioned in connection with the Swiss patent. Whenever such sections are selected very large relative to the groove length, the contact surface of the blade decreases so much that in the case of considerable peripheral force, excessive surface pressures with consequent damage of the contact surfaces has been found to develop.